In the past, personal recreational vehicles, such as snowmobiles, were powered by two-stroke engines. Two-stroke engines had been favored because of their relative simplicity, inexpensiveness, reliable cold weather starting ability, and high power-to-weight ratio. Use of two-stroke engines had drawbacks, however. Because two-stroke engines combust a fuel-oil mixture (oil is mixed with fuel for the sake of engine lubrication), they are less efficient and generate undesirable emissions. Such emissions are environmentally hazardous, unsightly, and acrid. Due to environmental considerations, manufacturers of snowmobiles are beginning to migrate away from two-stroke engines, using four-stroke engines, instead.
Four-stroke engines do not utilize a fuel-oil mixture. Rather, four-stroke engines combust unmixed fuel. With regard to engine lubrication, four-stroke engines make use of a separate oiling system with an oil pan located at the bottom of the engine. The oil pan forms a sump or reservoir in which oil used for lubricating the engine is collected or housed. An oil pump forces the oil from the oil pan through the internal mechanisms of the engine. Under the force of gravity, the oil drains back to the oil pan, whereupon it is again pumped throughout the engine.
Regardless of whether two-stroke or four-stroke engines were used, snowmobile manufacturers have sought to enhance the maneuverability and stability of the snowmobile. Maneuverability and stability are, in part, functions of the center of gravity of the snowmobile; the lower the center of gravity of the snowmobile, the greater the stability and maneuverability of the vehicle. The center of gravity of a snowmobile is greatly influenced by the placement of its engine. As the engine is mounted lower within the chassis, the center of gravity of the vehicle moves nearer to the ground. Thus, it is desirable to mount the engine as low as is possible (while still leaving minimally sufficient room for ground clearance).
One factor that frustrates the effort to mount a four-stroke engine at a relatively low point within its chassis is that the oil pan, which sits at the bottom of the engine, must make room for a steering shaft (or other form of stearing linkage). The steering linkage runs from the handlebars to a point beneath the engine, where tie-rods connect the steering shaft to the front skis. Accordingly, in the prior art, it has been necessary to mount the engine such that it is located above a segment of the steering linkage proximal to the tie-rods. As a result, the segment of the steering linkage proximal to the tie-rods has served as a boundary beneath which the engine could not be mounted (because the bottom surface of the engine would physically collide with the steering shaft).
For the aforestated reasons, it is desirable to devise a means by which an engine may be mounted at a low point in a chassis, yet still provide room for positioning of the steering shaft.